Polymer waveguides have been attracting attention in the construction of optical communication systems. Compared to attempts to fix a plurality of fibers in parallel fashion in an array, more reliable assemblies can be formed at lower cost by forming a polymer waveguide array all at once in a process using a polymer material in a polymer waveguide.
FIG. 1 is a perspective view used to explain the configuration of a single-mode polymer waveguide array assembly.
A waveguide array assembly has a waveguide array and a plurality of ferrules attached to both ends. A ferrule functions as a type of connector. Because they usually have a standard shape and size, they are used according to standards. In order to simplify the explanation, the ferrules will only be shown schematically.
The waveguide array has a plurality of cores and cladding surrounding the cores. Each one of the cores can individually guide single-mode light from one ferrule to another ferrule.
FIG. 2 is a perspective view used to explain how two single-mode polymer waveguide array assemblies are connected.
Two single-mode polymer waveguide array assemblies are connected to each other via the ferrules attached to both ends of the assemblies. The ferrules function as a type of connector when the assemblies are connected.
By coupling a plurality of single-mode polymer waveguide array assemblies in this manner, a waveguide can be continuously expanded as an optical communication system is constructed or expanded.
In a typical example, as shown in FIG. 2(A), two connected ferrules are secured by passing guide pins through guide pin holes provided in each ferrule.
In a typical example, the center of the guide pin holes are the absolute reference positions when two ferrules are connected to each other. However, the fixing method is not limited to this embodiment. If a different mechanical connection method is used, the configuration can be adapted to this difference. Therefore, the absolute reference position is not limited to this example, and can be in a different place.
Single-mode light is guided via each of the cores. Therefore, if the waveguides are to be continuously maintained when two ferrules are connected to each other, positioning accuracy between the cores is critical.
More specifically, in the connection plane (two-dimensional plane) between ferrules in FIG. 2(B), it is critical to keep the deviation in the planar positioning (x, y) from the absolute reference position to the center of the core, that is, the δx error and δy error, within an acceptable range. (Usually, y=0 when a single-layer waveguide array is used.)
FIG. 3 is a graph showing the relationship between positioning deviation from an absolute reference portion and coupling loss in a polymer waveguide for multi-mode light.
The core scale (diameter) in a multi-mode light polymer waveguide is known to be much larger than the core size in a single-mode light polymer waveguide. This is because the function of guiding single-mode light only is related to the wavelength of the guided light, and theoretically, is directly related to the core (diameter).
The multi-mode light example is cited here for qualitatively descriptive purposes only. However, significant coupling loss is known to increase as the amount of positional deviation increases. In the graph, the horizontal axis indicates the offset and the units are μm (microns), whereas the vertical axis indicates the coupling loss and the units are dB (decibels).
The following is an explanation of the method used to read coupling loss with reference to the graph of FIG. 3. As indicated by the difference symbols used in the plot, the coupling loss depends on the size (0 μm-50 μm) of the gap created between the connection planes of two ferrules (in the depth direction relative to the (two-dimensional) ferrule connection planes in FIG. 2(B)).
However, if the positioning error on the (two-dimensional) ferrule connection plane can be reduced to less than 5 μm in an ideal state in which the size of the gap has been suppressed to around 0 μm, a coupling loss reducible to less than 0.5 dB can be read.
However, even more stringent positioning accuracy is demanded when single-mode light is used. In theory, the positioning has to be at a very high level for the situation shown in FIG. 2 in which the positioning error is δx<0.5 μm-1.0 μm and γy<0.5 μm-1.0 μm. Otherwise, any positioning error leads directly to coupling loss.
Also, when the connection via ferrules is repeatedly extended, the coupling loss accumulates.
Patent Literature 1 discloses a manufacturing method for a resin-embedded waveguide element.
Patent Literature 2 discloses a waveguide mold and waveguide manufacturing method.
Patent Literature 3 discloses a stacked waveguide and manufacturing method for this stacked waveguide in which there are two or more light transmission paths, and any increase in crosstalk can be suppressed even when one of the transmission paths crosses another transmission path.
Patent Literature 4 discloses a manufacturing method for an optical waveguide array in which higher density integration can be achieved using a narrower pitch between optical waveguides.
Patent Literature 5 discloses an optical coupler able to achieve highly accurate alignment between a lens and optical waveguide using a simple configuration.
Patent Literature 6 discloses an optical waveguide component for easily connecting a multicore optical fiber and an optical element array with high density and low loss.
In Patent Literature 1-6, the problem addressed by the present invention is not addressed, which is to connect optical waveguide array assemblies with the very high accuracy demanded for single-mode light. Even an optical waveguide array assembly able to handle single-mode light has yet to be realized.